1. Field of the Invention
The present invention relates to an optical repeater that is preferable as a 1R repeater of optical communication.
2. Description of the Related Art
For lowering the cost of metro-access optical communication networks, WDM (Wavelength Division Multiplexing) communication having a large wavelength interval between channels (Coarse WDM communication) is expected to be widely used in the coming years. The wavelength interval in the Coarse WDM communication is approximately equal to or less than 20 nm. In this system, it becomes possible to lower costs for such reasons that it is not necessary to precisely control wavelengths of a light source and a filter, and a cooler used for keeping the temperature of a semiconductor laser of a light source is unnecessary because a certain amount of wavelength variation is tolerated.
In optical communication, an optical repeater is used for a purpose such as amplifying an attenuated optical signal. As the optical repeater, there exists a type in which a semiconductor optical amplifier and a gain equalizing filter are used. Regarding the semiconductor optical amplifiers, there exists a type in which a quantum well structure or a distorted quantum well structure is used for its active layer.
In a metro communication network over a long distance, a 1R repeater is indispensable to compensate for loss in each node of the metro communication network. A 1R repeater performs re-amplification of an optical signal and outputs it without converting it to an electrical signal.
Prior art is disclosed in Japanese Patent Laid-open No. 2000-40852 and in Japanese Patent Laid-open No. 2001-57455, for example.
However, in the Coarse WDM communication, the wavelength range (band) to be used is so wide as to range from 1.3 .mu.m to 1.6 .mu.m, so that it is impossible to be amplified by a single conventional optical amplifier (having a band of 0.05 .mu.m approximately), which increases the cost of amplifying the whole wavelength range. Consequently, conventional optical repeaters used in the Coarse WDM communication are also high-cost, so a cost reduction thereof has been desired.